Acoustical sensors can be utilized in chemical vapor deposition (CVD) systems to determine concentrations of select constituents. The basic operating principle of these instruments is to infer the concentration of the select constituent from differences in the time-of-flight of an acoustical signal through a test medium compared with that of a pure carrier. For example, in metalorganic CVD (MOCVD) systems, acoustical sensors find utility in the determination of bis-cyclopentadienylmagnesium (Cp2Mg) concentrations. Use of acoustical sensors in CVD applications generally are described, for example, at U.S. Pat. Nos. 6,116,080, 6,192,739, 6,199,423, and 6,279,379, and at U.S. patent application Ser. No. 13/705,650, the disclosures of which are hereby incorporated by reference herein except for express definitions contained therein.
Problems can arise when it is desired to accurately detect low concentrations of the constituent. A system that is tailored to address the challenges of low concentration detection in acoustical sensing systems would be welcomed.